In recent years, an optically active compound has been widely used for medicines, pesticides, sweeteners, liquid crystal materials, and the like. Various methods to manufacture the optically active compound have been researched and developed. For example, development of a special catalyst, and study of separation or disposal of unnecessary isomers has been conducted.
An optically active 3-chlorocarboxylic acid derivative which is halogenized at a β-position of a carboxylic acid is known as one of optically active compounds.
Known processes for producing optically active 3-chlorocarboxylic acid derivatives include:    (1) a process for producing an optically active 3-chlorocarboxylic acid in which hydrogen chloride is added to an α,β-unsaturated carboxylic acid by an addition reaction in the presence of cyclodextrin [J. Org. Chem., 55, 564 (1990)]; and    (2) a process for producing an optically active 3-chlorocarboxylic acid ester in which an optically active 3-hydroxycarboxylic acid ester and thionyl chloride are reacted in the presence of a catalytic amount of zinc chloride (Japanese patent Laid-open publication No. 63-222148; especially Example 4).
However, there are problems that the method (1) described above requires a long reaction, gives a low yield, and provides a low optical purity of the optically active 3-chlorocarboxylic acid. There are also various problems in the method (2) described above, that is, the method requires use of an excess amount of thionyl chloride and a long reaction time, gives a low yield, and uses a heavy metal salt as a catalyst. Besides such problems, there is no guarantee to be able to obtain a highly optically active 3-chlorocarboxylic acid ester.
An invention disclosed in Japanese patent Laid-open publication No. 11-246472 relates to a process for producing an optically active α-substituted carboxylic acid in which an optically active α-substituted carboxylic acid ester is used as a starting material, the optically active α-substituted carboxylic acid ester is contacted with an organic acid in the presence of an inorganic acid catalyst. A process for producing methyl D-2-chloropropionate, which is one of the optically active α-substituted carboxylic acid esters (the starting material of the process described above), in which L-methyl lactate and thionyl chloride are reacted without a solvent in the presence of a catalytic amount of pyridine is described in Example 1 of the publication.
However, according to the process described in Example 1 of the publication, the yield of methyl D-2-chloropropionate is not high.
The process described in Example 1 of the publication has been applied to production of an optically active 3-halogenocarboxylic acid ester (by the inventors of the present invention). The yield of the objective compound, i.e., 3-halogenocarboxylic acid ester, is low. An optically active 3-halogenocarboxylic acid ester having a high optical purity cannot be obtained at a high yield, that is, productivity by the process is not good.
An optically active 3-azido-carboxylic acid derivative which is obtained by azidizing a carboxylic acid at β-position and an optically active 3-aminocarboxylic acid ester which is obtained by hydrogenating the azide compound are known as optically active compounds in the same category (group) described above.
As a process for producing an optically active 3-azido-carboxylic acid ester, a process in which an optically active methyl 3-hydroxybutanoate is reacted with p-toluenesulfonyl chloride in pyridine to obtain an optically active methyl 3-(p-toluenesulfonyloxy)butanoate, and then the optically active methyl 3-(p-toluenesulfonyloxy)butanoate is reacted with sodium azide to obtain an optically active methyl 3-azide-butanoate, is known (“Tetraherdon Lett.”, 28, 3103 (1987), R&D Program for “Next-generation Chemical Process Technology, R&D Project for Process Utilizing Multi-phase Catalytic Systems, NEDO Annual Project Report 2000 (Heisei-13)”, pp. 33-45, The Japan Chemical Innovation Institute, Published June, 2001). In the above-mentioned “Tetraherdon Lett.”, a process for producing an optically active methyl 3-azide-butanoate by hydrogenating an optically active methyl 3-aminobutanoate is described.
However, there are problems in the commonly used processes explained above such as the reaction of the optically active methyl 3-hydroxybutanoate with p-toluenesulfonyl chloride being required to be performed in the presence of an excess amount of pyridine to produce the optically active methyl 3-(p-toluenesulfonyloxy)butanoate which is used as a starting material, and a side product of azidation, sodium p-toluenesulfonate, is necessary to be treated as a waste.
In the above-mentioned “Next Generation Chemical Process Techniques Development, Development of Multi-phase Catalyst Reaction Process Technique, Report of Completion in 2000 (Heisei-13)”, there is a description that the reaction of the optically active methyl 3-(p-toluenesulfonyloxy)butanoate and sodium azide is performed in (a) N,N-dimethylformamide, (b) a water-toluene system, or (c) a water-polyethylene glycol (interphase mobile catalyst phase)-toluene system. However, if the reaction is performed in (a), it is difficult to separate synthesized 3-azido-carboxylic acid ester from N,N-dimethylformamide because the boiling point of N,N-dimethylformamide used as the solvent is high. Moreover, sodium azide is not dissolved in N,N-dimethylformamide so that sodium azide has to react with the optically active methyl 3-(p-toluenesulfonyloxy)butanoate as a solid. Therefore, it is difficult to perform the reaction smoothly. If the reaction is performed in (b), a conversion rate from the optically active methyl 3-(p-toluenesulfonyloxy)butanoate to an azide compound is small, and the obtained optically active methyl 3-azide-butanoate does not have sufficient optical purity. If the reaction in (c) is performed, a conversion rate is better than that of the reaction performed in (b), but optical purity of the obtained optically active methyl 3-azide-butanoate is still not satisfactory high.
Japanese Patent No. 2912375 discloses a process for producing an optically active α-azide-carboxylic acid ester (concretely (R)-ethyl-2-azide-propionate) in which an optically active α-hydroxycarboxylic acid ester (an optically active 2-α-hydroxycarboxylic acid ester) which has a hydroxy group at the α-position and not the β-position is used as a starting material, the hydroxy group is converted to a p-toluenesulfonyloxy group, and is reacted with sodium azide to obtain the objective compound. However, this process also requires treatment of a side product of sodium p-toluenesulfonate as waste, and it is not guaranteed that an optically active α-azide-carboxylic acid ester having a high optical purity can be obtained.